1. The Field of the Invention
This application is directed to methods and devices for mixing and dispensing medical and dental compositions. More particularly, the application is directed to methods and devices for mixing and dispensing multi-part medical and dental compositions.
2. The Relevant Technology
Many modern formulations are packaged in two parts, often known as A and B components. Upon mixing, these A and B components typically undergo a chemical reaction which causes the resultant composition to "set up" in some desired manner. In the dental field, for example, several two-part formulations currently enjoy wide use such as glass ionomer cements and resinous luting cements. Dental impression materials are also typically made using A and B components.
In order to function properly, it is important that the A and B components of these two component systems be mixed together rapidly and thoroughly and in the right proportions. Failure to mix rapidly can result in loss of valuable working time with the resultant composition, and can impact the ability to obtain a thorough mix as the composition begins to set up unevenly. Failure to mix thoroughly can result in a composition having less than optimum characteristics. For example, if a poorly mixed composition is used as a cement, it is possible that portions of the cement will fail to reach the chemical strength required for a long-term bond.
Problems of obtaining rapid and uniform mixing are often complicated by differences in the A and B components. Often it is necessary to mix two liquids, while other times it is necessary to mix a powder with a liquid. Sometimes there are equal amounts of the A and B components, but other times there is more of one component than another. Additionally, the two components may have similar viscosities or widely differing viscosities.
The primary method employed for mixing A and B components has been simple mechanical mixing, through the use of a mixing bowl or pad and a stir instrument such as a spatula. This method tends to be somewhat messy and time consuming. It also is difficult at times to gauge whether the mixing has been sufficiently thorough.
It is also difficult in some instances to prevent formation of small air bubbles in the mixed composition. During the mixing process itself, the stirring action of the spatula, or similar mixing instrument, introduces and causes air bubbles to be entrapped within the mixed composition. Such entrapped air bubbles are usually detrimental.
Further, most dental compositions are ultimately dispensed from a syringe in order to control the amount dispensed, to permit precise placement of the dental composition and to prevent premature evaporation of constituents of the composition. This generally requires placement of the mixed compositions into a syringe. Additional air can become entrapped during this step.
Additionally, the simple process of mixing the components on a pad or in a bowl and then transferring them to a syringe takes time; this can lessen the available working time to actually utilize the composition. It is not uncommon for so much time to pass during the mixing and syringe-loading steps that the mixed composition becomes effectively unusable.
In an effort to overcome the time delays and the mess inherent in the approach set forth above involving mixing on a pad or in a bowl followed by loading into a syringe, attempts have been made to mix materials directly from a syringe or from a caulking gun. These attempts have involved the use of specially formed tips which effect some mixing as material is dispensed from the syringe or caulking gun. Although useful from the standpoint of minimizing the amount of time used to effect the mixing of A and B components, incomplete mixing is common.
According to one technique, A and B components are loaded in side-by-side fashion within a syringe barrel, such as with a dual barrel apparatus disclosed in U.S. Pat. No. 5,697,903 after which a mixer is inserted into the syringe barrel to mix the components. Following such mixing, the mixer is removed from the barrel and discarded. A plunger is then loaded into the syringe barrel to express the mixed material out of the syringe barrel. This technique requires that the mixer be initially placed into the barrel, then removed therefrom, often having residue of the mixture thereon, after which the plunger is placed into the barrel. These steps require the use of time, which is of the essence during the procedure.
What is therefore needed is an improved method and apparatus for mixing and dispensing compositions, particularly multi-part compositions.